Focused Interdigital Transducers Research Articles

Microfluidics-assisted synthesis of hydrogel microparticles with acoustic-magnetic control

Using one microfluidic device integrating acoustic and magnetic control, we propose a novel preparation method of magnetic fluorescent polyacrylamide hydrogel microspheres and calcium alginate hydrogel microparticles in this paper. The effect of the two interdigital transducers in different position on the droplets generation is studied. By tuning the input parameters of the two focused interdigital transducers (FIDTs), the excited focused surface acoustic wave (FSAW) can induce the generation of magnetic droplets with different sizes flexibly. Then the prepared magnetic droplets are cross-linked after crossing the continuous phase into the laminar flow induced by magnetic force. This method can avoid the direct reaction between the dispersed phase and the continuous phase in the channel, and enable the synthesis of magnetic fluorescent polyacrylamide hydrogel microspheres and calcium alginate hydrogel microparticles more easy and simple.

Noncontact Manipulation of Intracellular Structure Based on Focused Surface Acoustic Waves

Cell orientation is essential in many applications in biology, medicine, and chemistry, such as cellular injection, intracellular biopsy, and genetic screening. However, the manual cell orientation technique is a trial-and-error approach, which suffers from low efficiency and low accuracy. Although several techniques have improved these issues to a certain extent, they still face problems deforming or disrupting cell membranes, physical damage to the intracellular structure, and limited particle size. This study proposes a noncontact and noninvasive cell orientation method that rotates a cell using surface acoustic waves (SAWs). To realize the acoustic cell orientation process, we have fabricated a microdevice consisting of two pairs of focused interdigital transducers (FIDTs). Instead of rotating the entire cell, the proposed method rotates the intracellular structure, the cytoplasm, directly through the cell membrane by acoustic force. We have tested the rotational manipulation process on 30 zebrafish embryos. The system was able to orientate a cell to a target orientation with a one-time success rate of 93%. Furthermore, the postoperation survival rate was 100%. Our acoustic rotational manipulation technique is noninvasive and easy to use, which provides a starting point for cell-manipulation-essential tasks, such as single-cell analysis, organism studies, and drug discovery.

Development of heavy metal ions detector driven by surface acoustic waves

Environmental pollution caused by heavy metals is a global problem. Most of the metal ions lead to serious health concerns by producing free radicals. Therefore, rapid and accurate detection of metal ions has become an urgent problem. We develop a highly sensitive detector to detect heavy metal ions driven by surface acoustic waves (SAWs). The detector consists of a micro-reaction cell, a three-electrode system for electrochemical measurements, and two focused interdigital transducers (FIDTs) that produce SAWs. The SAWs promote liquid mixing effectively by sufficiently stirring the aqueous solution; therefore, the oxidation current in electrochemical reactions is enhanced. Furthermore, the center angles of the FIDT and the distance between two FIDTs turn out to be critical parameters in reaction efficiencies. These two factors can affect the SAW radiation areas which can influence the reaction efficiencies. This study realizes rapidly and accurately detecting heavy metal ions and provide a basis for designing SAWs-based detector for different chemical reactions. Environmental pollution caused by heavy metals is a global problem. Most of the metal ions lead to serious health concerns by producing free radicals. Therefore, rapid and accurate detection of metal ions has become an urgent problem. We develop a highly sensitive detector to detect heavy metal ions driven by surface acoustic waves (SAWs). The detector consists of a micro-reaction cell, a three-electrode system for electrochemical measurements, and two focused interdigital transducers (FIDTs) that produce SAWs. The SAWs promote liquid mixing effectively by sufficiently stirring the aqueous solution; therefore, the oxidation current in electrochemical reactions is enhanced. Furthermore, the center angles of the FIDT and the distance between two FIDTs turn out to be critical parameters in reaction efficiencies. These two factors can affect the SAW radiation areas which can influence the reaction efficiencies. This study realizes rapidly and accurately detecting heavy metal ions and provide a basis for desig...

Sorting of tumour cells in a microfluidic device by multi-stage surface acoustic waves

Abstract Detection of circulating tumour cells (CTCs) plays a crucial role in the diagnosis of tumour metastasis and evaluation of therapeutic effect on prognosis. The low number of the CTCs, however, makes their isolation from the peripheral blood very difficult. In this paper, a microfluidic device has been developed, which consists of a pair of straight interdigital transducers (IDTs) and focused interdigital transducers (FIDTs), to separate tumour cells from red blood cells (RBCs) in the blood stream by surface acoustic waves (SAWs). The standing SAWs (SSAW) generated by the straight IDTs enabled placing the CTCs and RBCs at the pressure nodes while the FIDTs generated the focused travelling pulsed SAWs (TSAWs) to push the CTCs away from the blood cells to achieve the isolation of CTCs. Using this mechanism, this device was capable of concentrating and separating 2 μm and 5 μm polystyrene particles and about 94.2% of particles with the diameter of 5 μm could be collected at the outlet. Moreover, 90% ± 2.4% of U87 glioma cells could be isolated from the RBCs when the cycle number of the TSAWs was 720 k. In the enrichment process, this microfluidic device totally relied on the SSAW without any additional assistance of the flow focusing. For the separation, unlike the bidirectional acoustic radiation force in SSAW, the unidirectional force generated by TSAWs consistently pushed the particles along the wave propagation, improving the sorting performance. This multi-stage device may provide an alternative method for sorting CTCs in a reliable and flexible manner.

A high-throughput acoustic cell sorter.

Acoustic-based fluorescence activated cell sorters (FACS) have drawn increased attention in recent years due to their versatility, high biocompatibility, high controllability, and simple design. However, the sorting throughput for existing acoustic cell sorters is far from optimum for practical applications. Here we report a high-throughput cell sorting method based on standing surface acoustic waves (SSAWs). We utilized a pair of focused interdigital transducers (FIDTs) to generate SSAW with high resolution and high energy efficiency. As a result, the sorting throughput is improved significantly from conventional acoustic-based cell sorting methods. We demonstrated the successful sorting of 10 μm polystyrene particles with a minimum actuation time of 72 μs, which translates to a potential sorting rate of more than 13,800 events per second. Without using a cell-detection unit, we were able to demonstrate an actual sorting throughput of 3300 events per second. Our sorting method can be conveniently integrated with upstream detection units, and it represents an important development towards a functional acoustic-based FACS system.

An optimisation of IDTs for surface acoustic wave sensor

Acoustic wave devices have been applied for detecting chemical and physical phenomena in gas and liquid applications. For the surface acoustic wave sensors (SAW sensors), the mechanical waves propagating through a piezoelectric crystal include Rayleigh and shear modes. They are influenced by the shape and size of the metal electrodes interdigital transducers (IDTs). Traditionally, IDTs were fabricated in the form of long straight parallel fingers on the piezoelectric substrate. This paper presents a piezoelectric device with focused IDTs (FIDTs) placed on a Y–Z lithium niobate (LiNbO3) substrate to achieve Rayleigh wave energy convergence. The energy conservation principle, called the Rayleigh principle, is used to prove the effective performance of IDTs with concentric shape. Amplitude fields of the conventional and concentric structures are shown. In addition, the energy loss and the output signal changes are compared between the two cases.

Milliseconds mixing in microfluidic channel using focused surface acoustic wave

A feasible approach of acoustic wave based ultra-fast homogeneous mixing in microfluidic channel is reported. After comparing simulation models of energy distribution between parallel interdigital transducers (IDTs) and concentric circular type focused interdigital transducers (F-IDTs), the F-IDTs were designed and built into microfluidic device to generate focused surface acoustic wave in a specific region of the microchannel. In the acoustic enhanced mixing region, continuous laminar flow was mixed efficiently in milliseconds by concentrated acoustic radiation. The active enhanced ultra-fast mixing was optimized and analyzed experimentally. This method could be developed for fast chemical or biochemical reactions and assays.

Design of efficient focused surface acoustic wave devices for potential microfluidic applications

Focused interdigital transducers (F-IDTs) patterned on surfaces of piezoelectric substrates can be used to generate surface acoustic waves (SAW) with high intensity and high beam-width compression ratio. A three dimensional coupled field finite element model of a focused SAW (F-SAW) device with interdigital transducers shaped as concentric circular arcs based on a YZ LiNbO3 substrate is developed in this study. This model was utilized to investigate the effect of geometric shape of transducers on the focusing properties of F-IDTs to identify the optimal design for potential microfluidic applications. The transducer design parameters investigated in the current study include number of finger pairs, degree of arc, geometric focal length, and wavelength of F-SAW. The transient response of the device on application of impulse and ac electrical inputs at the transmitting FIDT fingers were utilized to deduce the device frequency response and propagation characteristics of F-SAWs, respectively. The influence of applied input voltage on the propagation characteristics is also investigated. The insertion loss calculated for the various F-IDT designs was used to identify the optimal transducer configuration for sensing and microfluidic applications. The focusing properties as well as the wave propagation characteristics for the various F-IDT designs were evaluated in terms of the amplitude field and displacement contours generated in regions close to and at the focal point. Comparison with a conventional SAW device operating at megahertz frequency range and uniform IDT design is also made. Our study indicates that the focusing property of the device is significantly influenced by the geometric shape of the F-IDTs. The streaming phenomenon induced by F-SAW propagation, when in contact with a fluid medium, is discussed in detail. The simulated amplitude fields generated using ac analysis for the various designs in conjunction with wave propagation parameters derived using perturbational techniques such as Campbell–Jones are utilized to calculate the streaming forces and velocities based on successive approximation technique applied to Navier–Stokes equation (Nyborg’s theory). The maximum streaming force and velocity are obtained at the focal point of the F-SAW device. The magnitude of the generated streaming force and induced streaming velocity are strongly influenced by the transducer configurations. Based on the simulation results of this study, we provide guidelines for designing various F-IDTs to suite desired applications. F-SAW devices operating with higher applied input voltages and at higher frequencies, with optimal geometric length and larger degree of arc, are best suited for actuation and fluid microtransport.

Frequency response of a focused SAW device based on concentric wave surfaces: simulation and experiment

Focused interdigital transducers (FIDTs) based on concentric wave surfaces can excite surface acoustic wave (SAW) with high intensity, high beamwidth compression ratio and small localized area. In this paper, we developed a model to analyse the frequency response of a SAW device with FIDTs based on concentric wave surfaces. First, we constructed a focused SAW device by adopting a pair of FIDTs shaped as the concentric wave surface. To calculate its frequency response, a simulation model was established based on the 2D SAW filter model, effective permittivity approach and perturbation theory. Further, the focused SAW devices were designed and fabricated via the microelectromechanical system process technique. A good agreement between the simulated and measured results was found. Finally, the frequency responses of focused SAW devices based on concentric wave surfaces were discussed and some attractive features were found, such as less ripples of pass-band and high stop-band rejection. In addition, in comparison with the conventional SAW devices with uniform interdigital transducers, the focused SAW devices are more sensitive to variations in the focal area, instead of the whole delayline region. Accordingly, they are suitable to be applied to detect or manipulate some localized variations, such as acousto-optic or acousto-electric effects.

Analysis and design of focused interdigital transducers

Focused interdigital transducers (FIDTs) can generate surface acoustic wave (SAW) with high intensity and high beamwidth compression ratio. Owing to these features, they are very suitable to be used as the sources of microacoustic channels or waveguides in the near future. The focusing properties of FIDTs are dominated solely by their geometric shapes. Therefore, to obtain optimal performance, it is essential to analyze the FIDTs with a variety of geometric shapes. However, among the existing studies concerning the diffraction of FIDTs, a detailed analysis and design of FIDTs is still in paucity. In this paper, we adopted the exact angular spectrum of plane wave theory (ASoW) to calculate the amplitude fields of FIDTs on Y-Z lithium niobate (LiNbO3) with the shape as a concentric circular arc and the concentric wave surface. Based on the calculation results, we discussed the variations of the amplitude fields induced by changing number of pairs, degree of arc, and geometric focal length. In addition, the focusing properties of FIDTs on the (100)-oriented GaAs substrate were also analyzed and discussed. We also summarized the guiderules for designing a FIDT via four important factors. It is worth noting that the results of this study provide an important basis for designing various FIDTs to fit the desired applications.

SAW Convolvers Using Focused Interdigital Transducers

SAW Convolvers Using Focused Interdigital Transducers